I. Field of the Invention
This invention relates generally to an apparatus and method for delivering a drug to a patient's vascular system after performing a percutaneous transluminal coronary angioplasty (PTCA) procedure, and more particularly to an improved catheter arrangement which facilitates delivering and concentrating a drug to a treatment site in a blood vessel.
II. Discussion of the Prior Art
A percutaneous transluminal coronary angioplasty (PTCA) procedure typically consists of introducing a catheter with a single inflatable balloon into a patient's vascular system and positioning the balloon proximate a stenotic lesion to be treated. With the balloon juxtaposed relative to the blockage or constriction, an inflation fluid is introduced through a lumen of the catheter and made to inflate the balloon to expand the balloon against the blockage and to spread or open the obstructed blood vessel. This catheter is then removed and a second catheter is introduced into the vascular system. Subsequently, a medicament is introduced through the second catheter and to the site to treat the stenotic lesion to inhibit platelet aggregation at the site. This procedure is widely used in modern medicine and is far less traumatic than prior coronary bypass surgical procedures.
Certain drugs have been found to be more effective than others in reducing restenosis. These drugs help reduce the necessity of repeating the PTCA procedure. For instance, there are drugs which show a tendency to inhibit smooth muscle cell growth. Because these drugs can have undesirable side effects, it is not desirable that they be injected as a bolus dose into a peripheral vein and merely allowed to be carried by the blood stream to the situs of the stenotic lesion. However, and in accordance with the present invention, if that drug can be administered directly to the lesion, a significantly smaller dose may be employed and the side effects minimized.
Heparin is one such known drug for inhibiting clotting which can be delivered by injection as a bolus but which is known to have disadvantages. For instance, some patients, such as ulcer patients or patients with high blood pressure, are contraindicated for the administration of such large amounts of heparin. Other drugs, such as aspirin or persantin, are effective in inhibiting platelet aggregation at a treated site and thus to inhibit restenosis. Anti-coagulation medications and medications adapted to treat damaged arteries and to dissolve thrombus, are also preferably dispensed after the PTCA procedure.
One particular intravascular drug delivery dilation catheter ideally suited for a PTCA procedure is that disclosed in U.S. Pat. No. 4,994,033 which is assigned to the assignee of the present invention, the teachings of which are incorporated herein by reference. This particular catheter comprises concentrically arranged flexible plastic expander members with a space defined between the walls thereof for receiving a liquid medicament. A plurality of minute holes are formed through the outer expander member. When both expander members inflate, the drug is caused to be ejected out the tiny pores of the outermost expander member and against the adjacent tissue of the blood vessel. Using this device, a significantly smaller dosage may be employed to directly treat a stenotic lesion. This reduces the side effects of the particular medicament. During application of the medicament, the outer expander member is in direct contact with and seals against the blood vessel inner wall to restrict perfusion of blood through the interface. Thus, the medicament is not easily distributed throughout the entire body.
A balloon catheter for delivering therapeutic agents is disclosed in U.S. Pat. No. 5,049,132. This balloon catheter comprises a first balloon encompassed by a second balloon, the second balloon having a plurality of apertures defined therethrough for locally applying a medicament, such as heparin, to a stenotic lesion or a damaged coronary artery. This inflatable outer balloon is also adapted to seal against a blood vessel inner wall for a short time while the medicament is applied thereto. This device uses the medication as the balloon inflation fluid. The medication is administered in a volume and at a pre-determined pressure so that the balloon is expanded at a desired rate despite the leakage of medication through the apertures in the balloon wall.
Both of these prior art PTCA drug delivery catheters comprise two concentric balloons rather than a pair of balloons longitudinally spaced from one another along the catheter shaft. The drug delivery region in each device is defined through the outer wall of the outermost balloon, and thus, is positioned against the blood vessel wall in close conformity therewith. Both of these devices are adapted to allow medication to be slowly absorbed through a blood vessel wall proximate the balloon, and are not adapted to flush a large dose of a medicament past a treatment site to bathe the site.